The Brugada syndrome is a malignant form of ventricular arrhythmia that is associated with a high mortality rate of approximately 10% per year. It is believed to be responsible for at least 4% of all sudden deaths. Although important progress has been made in our understanding of the Brugada syndrome, significant gaps remain. Much of the dominating the theory on the pathophysiological mechanism of the syndrome is based on a few studies using perfused ventricular wedges. The way by which the Brugada-like ECG is generated in these studies is questionable, and the proposed ionic mechanisms have not been vigorously tested. Our goal is to bridge these gaps by delineating the role of Ito and late INa in the cellular electrical abnormalities as well as contractile dysfunction of the Brugada syndrome. A second goal of our study is to explore potential new therapeutic strategies for the treatment of the disease. [unreadable] [unreadable] Our specific aims are 1) to determine the role of Ito in generating the AP abnormalities in the Brugada phenotype. We will examine whether Ito, when coupled with a reduced Na+ current, is sufficient to produce the abnormal epicardial AP repolarization properties in Brugada syndrome, and whether blockade of Ito restores the normal AP morphology. 2) To determine the ionic basis of the contractile abnormality in Brugada syndrome. Wall-motion abnormality has been described in Brugada patients, and the basis of such abnormality is directly relevant to our understanding of the arrhythmogenic substrate of the disease. We will examine myocyte contractile and Ca2+ transient abnormalities under Brugada cellular electrical settings. And 3) to determine the role of late INa in the AP abnormalities in the Brugada syndrome. We will examine whether reduction of the late INa in addition to the fast Na+ current is required to produce the abnormal AP morphology of the Brugada syndrome, and test the therapeutic potential of restoration of the late INa as a treatment of the syndrome. The key approach we employment is a novel technique, the dynamic clamp. It will allow us to selectively and quantitatively manipulate the conductance of interest in single myocytes, and gain in depth knowledge of the cellular mechanisms of the Brugada syndrome. Our proposed study closely fits the stated purpose of the R21 Program Announcement because it is innovative and exploratory, and it is consistent with the goal of the funding program. [unreadable] [unreadable] [unreadable]